Why is it that a man feels at his sexiest when he wakes up in the morning but a woman wants to go back to sleep?

And why, late at night, when a woman is in the mood for love, is her man just lying there, snoring? It all comes down to hormones. Here’s why our sex clocks don’t always tick in time.

5am

Even before a man has opened his eyes in the morning, his level of testosterone is at its peak – between 25% to 50% more than at any other time of the day.

That’s because the pituitary gland in his brain – which governs the production of the male sex hormone – has been switched on in the night and levels have been steadily rising until dawn.

Women also make ­testosterone – the main sex drive hormone – but produce a fraction of the amount and it rises by only a tiny bit overnight. It is also kept in balance by oestrogen and progesterone.

“Men need only a normal amount of testosterone to feel like sex,” says Ashley Grossman, neuroendocrinology professor at St Bartholomew’s Hospital, London. “The raised levels in the morning means most men will wake up two to three times a week with erections.”

6am

Slept well? A good kip is another reason a man may feel even more amorous in the morning. Studies found the longer and deeper a man has slept, the higher his testosterone levels. Research in the Journal of the American Medical Association shows getting more than five hours’ sleep can raise male levels by an extra 15%.

7am

While a man’s levels of sex hormones are at their highest when he wakes up, a woman’s are at their lowest. “Male and female testosterone levels are at their highest at opposite ends of the day, so they are out of synch,” says consultant gynaecologist Gabrielle Downey, of the Sandwell and West Birmingham Hospitals NHS Trust.

“It takes more than hormones to get a woman in the mood, so men need to make an active effort.”

Instead, women’s hormones rise and fall more over their monthly cycle than through the course of a day.

At their height – midway through her cycle – a woman’s levels of testosterone will be 30 times higher than at the start.

8am

Preparing for another busy day at work?

As both sexes get ready for the day, levels of the stress hormone cortisol rise to help them wake up – and help dampen the effect of sex hormones.

After this initial surge, if the body keeps producing too much in response to stressful events over the day, studies have found it lowers the sex drive of both men and women.

9am

As the day goes on, men will keep steadily making testosterone in their testes. The hormone is also needed to trigger muscle growth and sperm production. Although men are mostly unaware of it, levels will fall and rise in a wave naturally every 90 minutes throughout the day as part of the body’s in-built body clock.

12 noon

An attractive colleague wanders into the workplace. But it won’t be a man’s hormones that react first. If a man feels highly attracted by someone, it’s his nervous system that kicks into action.

The sight of someone ­attractive immediately releases feel-good brain neurotransmitters called endorphins – and triggers blood flow to a man’s genitals. Sex hormones take longer to increase. However, when confronted with a sexy person, a man who naturally already has higher testosterone levels is likely to be more flirtatious with them.

Men with more testosterone are also more likely to be found attractive by women, according to researchers at Wayne State University in Michigan, US.

According to assistant professor of psychology Richard Slatcher – who has studied the link between testosterone and attractiveness in men – the more ­testosterone a man has, the more women are likely to say they click with them.

1pm

If women are lucky enough to catch a glimpse of the Diet Coke hunk at ­lunchtime, they are less likely to be aroused than if a male colleague sees someone he fancies. Instead, studies have found that a woman’s testosterone levels are more likely to be boosted by the anticipation of sex with her own partner.

In one study by the University of Texas, women in long-distance ­relationships gave five saliva samples. The tests were given two weeks before they saw their partners, the day before, before sex, the day after sex and three days after the pair were separated. The women’s testosterone levels hit their peak the day before they were due to see their partners again.

6pm

As evening approaches, men’s levels of testosterone are starting to fall while women’s sex hormones are gradually rising, albeit much more slowly.

However, an after-work gym session can boost the libido of both genders. Studies have shown that testosterone levels in men are significantly higher after 30 to 40 minutes of intense ­resistance or endurance exercise.

Research by scientists at the University of California, San Diego, found men who exercised had a boosted libido.

They also reported having 30% more sex and 26% more orgasms.

Levels of sex hormones also spike in women after exercise. According to a study by the University of Texas, women who had 20 minutes of cardio exercise were more aroused by seeing an erotic film than women who had not exercised.

7pm

When it’s time to unwind after a stressful day, even putting on a CD to relax can affect sex hormone levels.

A Japanese study by Nara University found that music – including pop music, jazz or just a compilation of favourite songs – boosted testosterone levels “significantly” in women but had exactly the opposite effect in men.

Researchers believe the reason is that music may make women feel more relaxed, bonded and in turn more sexual, while in men it calms their aggression and in turn reduces their levels of testosterone.

8pm

If an important match is on TV, the results can also affect a man’s testosterone – depending on the result.

According to a study of saliva tests by the University of Utah, sports fans watching a World Cup game boosted hormone levels by about 20% if their team won.

After a loss in a big game, there was a 20% drop in levels. Not good news for England fans, then!

By contrast, women are more likely to be affected by actually playing sport rather than watching it.

In one study of women athletes, their testosterone levels significantly increased after long runs.

9pm

By now, a man’s ­testosterone level is dropping to the lowest level of the day, while a woman’s is heading towards its highest point.

But the more attractive a woman feels, the more likely it is that she will want to jump into bed with him.

“Sexual desire in women is not a simple story,” explains Gabrielle Downey.

“For men, it’s more down to testosterone. For women, the single greatest factor i­nfluencing a woman’s sex drive is body image and how attractive she perceives herself to be.

“It means that if a woman sees herself as unattractive, she is much less likely to want to have sex.

“That’s why women with polycystic ovaries, who have increased levels of ­testosterone, don’t have increased libido.

“They often see themselves as overweight and not attractive – and that feeling ­overrides their heightened sex hormones.”

10pm

Even though men’s testosterone levels are now at their lowest, they are still more likely to have sex in the evening.

“It’s been said that women need a reason and men just need a place – and I think that’s true,” says Gabrielle.

“Even though male testosterone may have dipped, their levels are still running higher than a woman’s so they are still responsive – even though the man’s levels were higher when they first woke up that morning.” Once they are making love, if a woman’s testosterone levels are peaking because of where she is during her cycle – around the 13th day – her orgasms are more intense and they will be felt all over the body.

When the levels are lower, her climaxes are less intense and centred mainly around the sexual organs.

11pm

During orgasm, the bonding hormone oxytocin is released – which helps to bring couples closer.

In males, the bonding hormone helps make the prostate and seminal glands to contract.

In women, it helps to spark uterine contractions that move the sperm towards the ovaries.

The release of oxytocin after sex also explains why men are notorious for falling asleep after making love.

“In women, oxytocin is known as the hormone of breast-feeding and muscle contractions,” says Gabrielle.

“But in men the extra boost of oxytocin has also been found to work as ­a neurotransmitter in the brain and may also promote sleep.”

Oxytocin’s bonding effects will last after sex, too.

In one study, Swiss researchers gave 47 couples a nasal spray containing either oxytocin or a placebo.

The pairs were then videotaped, discussing subjects that they usually rowed about.

The partners who were given oxytocin were more reasonable and less aggressive with each other.

Oxytocin was also found to have an “amnesiac” effect – which may also have allowed them to forgive each other more easily after rows!